ABS Exam 2 (5- Tetropod Origins)

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  1. From Fins to Limbs
    ___ -> ___ -> ___
    “Rhipidistia” -> “Labyrinthodonts” -> Tetrapods
  2. Acanthostega – “four-footed fish”
    • Mostly aquatic – internal gills
    • Radial fin rays supported tail
    • Lateral line system
    • Labyrinthodont teeth
    • Intracranial joint
    • Weight-bearing girdles
  3. Panderichthys (Elpistostegidae)
    • Eyes on top
    • No anal/dorsal fins, reduced tail fin
    • Body and head – dorsoventrally flattened
    • Long snout
    • Derived humerus = powerful forelimbs for propping
    • Ventrally-projecting ribs
  4. Late Devonian “Fishapod” -
    • Tiktaalik
    • Derived Epistostegid
    • Claim to fame: Filled gap between most derived Sarcopterygian and first tetrapod.
    • Intermediate characters between fish and tetrapod
  5. Tiktaalik fish like features
    • Fin rays
    • Well-developed gills
    • Poorly ossified vertebrae
    • Long body
  6. Tiktaalik tetropod-like features
    • No operculum
    • Large, overlapping ribs – support body out of water
    • Long snout
    • Pectoral fin with bend in middle – prop body up
    • Fingerlike bones at end of fin
  7. The Earliest Tetrapods
    Primarily aquatic:
    Presence of groove on ventral surface of ceratobranchials: -> Supports gills in fishes and internal gills
  8. animal with fish-like internal gills;maybe had lungs
  9. Humerus branches to form
    radius and ulna
  10. Preaxial =
    segmentation of radius, radiale
  11. Postaxial =
    segmentation & branching to form carpals, metacarpals, digits
  12. Hypotheses for terrestrial living
    • Limblike fins of Devonian Sarcopterygians allowed walking from one dry pond to a larger one
    • Searching for food
    • Juvenile dispersal
    • Laying eggs in moist environments
    • Basking in sun to raise body Temp
  13. Adaptations to life in a shallow water environment
    • Limbs with digits
    • Development of ankles and wrists
    • Attachment of pelvic girdle to vertebral column
    • Development of a distinct neck (loss of opercular bones)
    • Articulation between skull and vertebral column
    • Longer, flatter snout
  14. Living fish that provides a model of tetrapod-like limb usefulness in water.
    • Frogfish
    • Modified pectoral fin to walk over substrate
  15. Extant non-amniotic tetrapods
    (frogs, salamanders, caecilians)
  16. Primitive Paleozoic tetrapods:
    • Larger than living amphibians
    • Many had dermal scales(no cutaneous gas exchange)
    • More closely related to amniotes than amphibians
  17. Devonian Tetrapods:
    • Acanthostega
    • Icthyostega
  18. Acanthostega Primitive features
    • Fin-like forelimb and hindlimb
    • Operculum (internal gills)
    • Weak zygapophyses
    • Small ribs
    • Non-bendable elbow
    • Weak sacral connection
    • Large tail fin
  19. Ichthyostega
    • More specializations for both aquatic AND terrestrial life
    • Distinct thoracic and lumbar regions
    • Longer, overlapping ribs (only thoracic)
    • Elongated ribs at base of tail
    • Hindlimb like seal flipper
    • Ear region specialized for underwater hearing
  20. Current classification of Paleozoic non-amniote tetrapod:
    • Temnospondyls: more aquatic, immobile skull, flatskull, 4 fingers
    • Anthracosaurs: more terrestrial, domed skull, 5 fingers
  21. Early Carboniferous : tetrapods had split into 2 lineages:
    • Batrachomorphs
    • Reptilomorphs
  22. Reptilomorphs
    • non-amniotic relatives
    • amniotes - Synapsid Testudine Archausoromorph Lepidosauromorpha
  23. Batrachomorphs
    • Temnospondyls – nonamniotic tetrapods
    • Largest, longest-lasting group Primitive, extinct
    • amphibia
  24. Temnospondyls
    only group of non-amniotic tetrapods(aside from amphibians) to survive the Paleozoic
  25. only group of non-amniotic tetrapods(aside from amphibians) to survive the Paleozoic
  26. Anthracosaur
    (non-amniotic reptilomorph) tetrapods
  27. Lepospondyls
    (Reptilomorphs) but may be moreclosely related to living amphibians or even amniotes.
  28. Great diversification of insects in the Late Carboniferous (in response to increasing diversity of vegetation?)
    Supported diverse fauna of fully terrestrial vertebrate predators!
  29. amniotic egg advantages
    • freedom from aquatic environment
    • skip the stage between egg an adult
  30. Derived Features of Amniotes
    • Amniotic egg
    • Skin permeability: Keratin, Lipids, Skin elaborations (hair, scales, feathers)
    • Costal (rib) ventilation of lungs
    • More complex innervation of forelimb
  31. Structure and Development of the Amniotic Egg
    • Shell
    • Albumin
    • Large yolk
  32. amniotic egg Shell
    leathery or calcified, mechanical protection, butporous to allow movement of respiratory gases, water vapor
  33. amniotic egg albumin
    (egg white) protection, reservoir of water, protein
  34. Large yolk
    energy for the developing embryo
  35. Amniotes have 3 additional membranes:
    • Chorion – surrounds entire contents
    • Amnion – surrounds embryo
    • Allantois – storage of nitrogenous waste, respir. organ
Card Set
ABS Exam 2 (5- Tetropod Origins)
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